1. Field of the Invention
The present invention relates to a branched type light transmission system including a plurality of bundled light transmission tubes each comprising a flexible cylindrical cladding and a transparent core filled in the cladding and of which the refractive index is higher than that of the cladding.
2. Description of the Prior Art
Light transmission tubes comprising a flexible cylindrical cladding and a transparent core filled in the cladding are known from the disclosures in the U.S. Pat. Nos. 3,814,497(Stone), 4,009,382(Nath) and 5,333,227(Ishiharada et al).
Stone discloses a liquid core multimode optical waveguide including a plurality of parallel spaced hollow fused quartz fibers each of which forms a light transmission tube. The fiber consists of a main body (cladding) and an organic liquid core filled in the main body. The liquid core is tetrachloroethylene or a mixture of tetrachloroethylene and carbon tetracloride.
Nath discloses a flexible light guide comprising a flexible hollow tube of plastic material, light transmissive means closing the tube at its ends and a light conducting liquid which has a refractive index greater than that of the plastic material of the tube and which completely fills the flexible tube between the light transmissive means to form a closed liquid light guide system. The light transmissive means is a window made of quartz or quartz glass. The light conducting liquid is an aqueous solution of an inorganic salt.
Ishiharada et al discloses an optical waveguide hose including a hollow tubular cladding, a fluid core in the cladding, the fluid core having a higher index of refraction than the cladding, and sealing plugs fitted in opposite end openings of the cladding.
In all the prior-art light transmission tubes, a fluid is filled in a cladding and the cladding is sealed at either end thereof with a hard light transmissive window or sealing plug. To prevent the light-incident portion of the light transmission tube from being thermally broken or contaminated when light is incident from a high-power light source upon the tube, the window or sealing plug is made of an inorganic glass such as quartz glass. Pyrex grass, multicomponent glass or the like. Such light transmission tubes are bundled at the light-incident end for light transmission from a single light source upon the plurality of light transmission tubes. It has been tried to branch each of the light transmission tubes. A typical prior-art light transmission tube is shown in FIG. 1. As shown, a fluid core is filled in a flexible cylindrical cladding 101 and the cladding 101 is sealed at either end thereof with an inorganic glass sealing plug 102 to form a light transmission tube 100. Two such light transmission tubes 100 are bundled together at the light-incident ends thereof with a binding member 103. Light is incident from a high-power light source upon the end of the bundled tubes 100 for light transmission through the tubes 100.
In the prior-art light transmission tube shown in FIG. 1, since the inorganic glass sealing plugs 102 provided at the light-incident ends of the tubes 100 are not deformed due to any external force, the binding member 103 and tubes 100 define clearances 105 between them. When a light is incident upon these clearances, it cannot be efficiently incident upon each tube 100. In this prior-art light transmission tube, the filling rate of the tubes 100 in the binding member 103 is about 50%, which cannot assure any high efficiency of light incidence upon the tubes 100.